For over 400 years Cartesian divers have been used to illustrate to students the physical principles of density and buoyancy. Classic Cartesian divers are named for the French scientist Rene Descartes. In a classic Cartesian diver, an external gas chamber is filled with liquid. In classroom experiments this is typically done in a 1.5 liter plastic soda bottle. The squeezing of the bottle then exerts pressure on the liquid. Inside the container is housed a smaller container, i.e. the “diver.” The diver has air trapped inside of it. With pressure exerted on the external liquid in the outer container, the squeezed liquid does not compress, but the air trapped inside the diver does. With the change in volume of trapped air, the diver then rises or sinks relative to the pressure of the outer liquid.
An object is buoyant in water due to the amount of water is displaces or “pushes aside.” If the weight of the water that is displaced by an object in water exceeds the weight of the object, then the object will float. As pressure is applied to the outer liquid, pressure is also applied to the air pocket trapped inside the diver, thereby reducing the size of the air pocket. As the bubble size reduces, the driver becomes less buoyant and begins to sink. As the pressure is released, the air bubble grows and becomes more buoyant, causing the diver to rise back to the top of the liquid.
A submarine uses this principal in a slightly different way. The submarine contains ballast tanks that can be filled or emptied of air. The air that moves to and from these tanks is at the current pressure of the water outside of the submarine. A submerged submarine that is at a steady state, neither rising nor sinking, will rise when air is introduced into the ballast tank or sink when air is removed from the ballast tank because this movement of air causes changes in the submarine's buoyancy.
The prior art involving the use of these physical principles utilize an outside container that absorbs the pressure change, thereby effectuating the falling and rising of the diver. A Cartesian toy that allows the floating diver to move in a horizontal direction as well as the classic vertical direction is disclosed by Seefluth in U.S. Pat. No. 4,455,782, but this invention is limited to the exertion of pressure upon the outside liquid container itself. This limits the usefulness of the diving device outside of the context of closed, relatively small liquid containers. Currently, there is nothing on the market that allows an object to dive in a large body of water, such as a bathtub, swimming pool, pond or lake that will then wait for a period of time before resurfacing. Therefore, a need exists for such a system.